1. Field of the Invention
The present invention relates to a communication system, and more specifically, to a symbol acquisition apparatus and a method thereof.
2. Description of the Prior Art
Initially an ultra wideband (UWB) communication system was applied to military affairs. In recent years, the requirements of high-speed exchange techniques have rapidly increased. Hence, for the low-cost communication products, UWB communication systems have become more popular. In general, the bandwidth of UWB communication system is larger than 20% of the value of the related central frequency. That is, assume that the central frequency of the transmitted signal is 6 GHz and the transmitted bandwidth of the communication system is more than 1.2 GHz, and the communication system can be viewed as a UWB communication system. Compared with the signal bandwidth, 1.25 MHz, utilized by CDMA system, the UWB communication system is 1000 times bandwidth of the CDMA system.
The information of a traditional RF transmission is carried by a continuous wave. However, the UWB communication system utilizes a very short pulse wave to transmit information. Each pulse wave continues only about 1/1013 second. In this way, the energy provided by the UWB communication system distributes over a very broad band, rather than being clustered around a single carrier frequency. Therefore, the energy distribution on a unit bandwidth of the UWB communication system is substantially lower than the energy distribution of the related art communication technique. However, the UWB communication system lacks good ability of piercing through an obstacle. Additionally, it is easily affected by a multi-path effect and interfered by other wireless communication system.
Taking IEEE 802.15.3a specification as an example, there are four preamble symbols at the front end of a received packet. A related art UWB communication system perform a cross correlation on the four preamble symbols of the front end of the packet by match filter, and determines a preamble symbol boundary according to a maximum value of the calculating results. Because the above-mentioned preamble symbols are transmitted on different bands, the UWB communication system generates symbol boundaries corresponding to the preamble symbols. However, due to the UWB communication system is easily affected by the multi-path effect, the above-mentioned calculating results may contain a plurality of peek values. In this way, the system may misjudge the position of the maximum value and further generate a wrong symbol boundary. Additionally, comparing with other wireless communication systems, the energy of the UWB communication system is distributed over a broader band. Hence, when the band utilized by the UWB communication system overlaps the surrounding band utilized by other wireless devices, the signal-to-noise ratio (SNR) will be substantially reduced, further influence signal qualities and lower the correctness of the generated symbol boundaries.